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| United States Patent |
5,284,633
|
|
Gefvert
|
February 8, 1994
|
Solvent extraction of precious metals with hydroxyquinoline and
stripping with acidified thiourea
Abstract
The invention relates to the use of a single solvent extraction reagent
which greatly simplifies the recovery of platinum, palladium and gold from
base metal-containing solutions. The recovery of platinum, palladium and
gold from acidic feed solutions which contain chloride ion is accomplished
by first using a substituted 8-hydroxyquinoline reagent or a derivative
thereof for extraction wherein a chelate is formed between the reagent and
the precious metals. The chelated product is sufficiently stable to allow
any base metals or complexes thereof to be scrubbed from the organic
phase. The precious metal values are then recovered from the reagent by
stripping with acidified thiourea solution.
| Inventors:
|
Gefvert; David L. (Dublin, OH)
|
| Assignee:
|
Sherex Chemical Co., Inc. (Dublin, OH)
|
| Appl. No.:
|
975504 |
| Filed:
|
November 12, 1992 |
| Current U.S. Class: |
423/22; 423/24 |
| Intern'l Class: |
C01G 055/00; C22B 011/00; B01D 011/00 |
| Field of Search: |
423/22,24
|
References Cited
U.S. Patent Documents
| 3967956 | Jul., 1976 | Payne | 423/22.
|
| 3985552 | Oct., 1976 | Edwards | 423/24.
|
| 4041126 | Aug., 1977 | Baltz et al. | 423/22.
|
| 4571266 | Feb., 1986 | Konig et al. | 423/22.
|
| 4654145 | Mar., 1987 | Demopoulos et al. | 423/24.
|
| 4698429 | Oct., 1987 | Kokko et al. | 423/24.
|
| 4913730 | Apr., 1990 | Deschenes et al. | 423/22.
|
| 4942023 | Jul., 1990 | De Schepper et al. | 423/24.
|
| 5045290 | Sep., 1991 | Harris et al. | 423/22.
|
Primary Examiner: Langel; Wayne
Assistant Examiner: Bos; Steven
Attorney, Agent or Firm: Scully, Scott, Murphy & Presser
Claims
What is claimed is:
1. In the extraction and separation of one or more precious metals from a
dilute aqueous chloride feed solution thereof which also contains
contaminant metal values, by contacting said feed solution with a liquid
ion exchange reagent to load said one or more precious metals and
contaminant metal values and stripping said one or more precious metals
from the reagent, the improvement comprising:
a) extracting the one or more precious metals with a single solvent
extraction reagent under conditions effective to form a chelate between
said reagent and said one or more precious metals wherein said single
solvent extraction reagent comprises a 7-substituted-8-hydroxyquinoline
compound or derivative thereof having the formula:
##STR2##
wherein R is a linear, branched or cyclic alkyl, alkenyl, vinyl, aryl,
cycloalkyl, or cycloalkenyl group, containing from about 6 to about 20
carbon atoms;
b) scrubbing said contaminant metal values from the precious metal loaded
reagent; and
c) stripping the single solvent extraction reagent with acidified thiourea
solution to recover one or more precious metals.
2. A process according to claim 1 wherein said one or more precious metals
are selected from the group consisting of gold, silver, platinum,
palladium, rhodium, osmium, iridium, ruthenium, and mixtures thereof.
3. A process according to claim 2 wherein said precious metals are
platinum, palladium and gold.
4. A process according to claim 3 wherein said feed solution contains from
about 1 to about 5000 ppm of gold, from about 1 to about 5000 ppm of
palladium, and from about 1 to about 1000 ppm of platinum.
5. A process according to claim 1 wherein said contaminant metal values are
selected from the group consisting of Pb, Al, Ba, Ce, Zr, Fe, Cu, Ni, Mo,
Sn, Sb, As, Bi, Zn and mixtures thereof.
6. A process according to claim 1 wherein said acidified thiourea solution
contains from about 1M to about 4M HCl.
7. A process according to claim 6 wherein said acidified thiourea solution
contains at least 0.01M thiourea.
8. A process according to claim 7 wherein said acidified thiourea solution
contains from about 0.01 to 2M thiourea.
9. A process according to claim 1, further comprising, following step (c),
separating a solid product comprising the stripped precious metal values
from said acidified thiourea solution.
10. A process according to claim 9 wherein said separating step comprises
hydrogen reduction of said solution to cause said solid product to form.
11. A process according to claim 9 wherein said separating step comprises
adding a precipitating agent to said acidified thiourea solution to cause
said solid product to form.
12. A process according to claim 11 wherein said precipitating agent is
sodium hydroxide.
Description
FIELD OF INVENTION
The present invention relates to a method for extracting and concentrating
gold, platinum and palladium from acidic solutions which contain chloride
ions by using a liquid-liquid extraction process, wherein a single
extracting agent is employed. A preferred aspect of the present invention
involves the use of alkylated 8-hydroxyquinoline reagents or derivatives
thereof to extract gold, platinum and palladium from acidic solutions
containing chloride and base metal ions obtained from leaching of ores,
catalysts or other precious metal containing materials wherein the
extracting agent is scrubbed to remove base metal contaminants and
stripped with thiourea to produce a solution containing the precious
metals free of base metal.
BACKGROUND OF ART
In recent years, a growing demand for precious metals in high-technology
applications and the increasing cost of precious metals has made the
practice of recovering and refining these metals very important. To meet
these demands, industry is turning to new sources of precious metals such
as complex sulfide ores, and recycling precious metals from catalysts and
electronic scrap.
Using traditional smelting techniques to treat these materials is not
always effective due to their refractory nature and low precious metal
content. Leaching with acidic chloride solutions containing an oxidizing
agent is effective in removing the precious metals and has the added
advantage of preserving valuable substrates for recycling. The recovery
and subsequent separation of precious metals from the chloride feed
liquors constitutes a difficult refining problem.
The recovery and subsequent separation of precious metals from these
chloride feed liquors constitutes a difficult refining problem. These
liquors generally contain low levels of precious metals (ppm levels) and
high levels (on the order of grams per liter) of base metals such as iron,
copper, zinc, tin, and nickel. Moreover, the volumes of solutions
generated are large compared to the volume of highly concentrated
solutions generated from typical precious metal refining. Classical
precipitation techniques are inefficient when applied to such solutions
and they are being replaced by modern separation methods. Among the
latter, solvent extraction (SX) processes are being considered for the
separation and extraction of precious metals by industrial companies.
Solvent extraction is sometimes referred to as liquid ion exchange
extraction and it is being utilized as a promising new method in
extraction and separation science. Briefly, this process is basically
described by two steps. In the first, the extraction step, dilute aqueous
feed solution which contains the metal ion to be recovered is mixed with
an immiscible hydrocarbon diluent or carrier containing an ion exchanger
or ligand dissolved therein, and the resulting metal complex migrates to
the organic phase. In the second, the stripping step, the separated
"loaded" organic phase is mixed with an aqueous solution of a stripping
agent (e.g., sulfuric acid) and the procedure is reversed, the metal ion
passing back to the new aqueous phase. As a consequence, the dilute feed
solution is converted into a highly concentrated solution, from which the
metal values are more readily recovered, e.g., by electrolysis. The barren
organic phase is then essentially recycled through the system.
The current SX technology as it is applied to precious metals refining
calls for Au, Pt, and Pd to be extracted by separate solvents or other
techniques. Gold, for example, is removed first by SO.sub.2 reduction to
the metal or extraction using ketones (MIBK) or esters (DBC). Palladium is
then extracted using alkyl sulfides or oximes and platinum is removed
using tributyl phosphate (TBP).
Despite the relatively good performance of SX processes in precious metal
refining, there are some serious complications which need to be solved if
SX is to be successful in separating gold, platinum and palladium from
base metal rich liquors. The major drawbacks
Despite the relatively good performance of SX processes in precious metal
refining, there are some serious complications which need to be solved if
SX is to be successful in separating gold, platinum and palladium from
base metal rich liquors. The major drawbacks to reagents used in precious
metal refining operations are kinetics and selectivity. The extraction of
palladium by sulfides or oximes suffers from slow kinetics. This is not an
economic burden when the treated volumes are small. However, when large
volumes of dilute solutions are treated the large inventory of reagent
required for prolonged contact times becomes uneconomic. TBP extraction
for platinum suffers from poor selectivity to other base metal chlorides
and also requires high acidities to work well. The cost in acidifying
large volumes of solution make this approach uneconomic.
U.S. Pat. No. 4,654,145 teaches a new technique for separation of gold,
platinum and palladium based on using alkylated derivatives of
8-hydroxyquinoline. In this process the precious metals are extracted from
acid chloride solutions using an alkylated 8-hydroxyquinoline such as
Kelex 100. The metals are then separated using differential stripping.
Platinum is stripped using water, gold is recovered by hydrolytic
stripping or hydrogen reduction, and palladium is recovered using hydrogen
reduction or acidic stripping. This prior art does not address the effect
of base metal extraction on the differential stripping techniques
employed. Iron and copper will extract with the precious metals and
contaminate the water wash and hydrogen reduction steps.
U.S. Pat. No. 5,045,290 teaches the extraction and purification of platinum
and palladium from base metal chlorides using alkylated
8-hydroxyquinoline. This process utilizes pH controlled scrubbing to
remove acid and base metal chlorides. Platinum is recovered by a pH
controlled wash and palladium is recovered by 8N HCl stripping. This prior
art doe not consider gold extraction and stripping or how gold behaves
during the base metal wash stages.
The prior art is not well suited to extraction of gold, platinum, and
palladium present in small amounts from base metal chlorides present in
large amounts. Current precious metal refining utilizes a separate reagent
for each precious metal while processes using only one reagent rely on
selective stripping of the precious metals. Multiple reagents and
selective stripping add unnecessary complication and expense to the
removal of trace amounts of precious metals.
In view of the deficiencies of the current available reagents used to
extract precious metals, a more efficient and economical means must be
developed. One of the objects of the present invention is to employ a
single reagent to extract and a single strip stage to concentrate the
precious metals after the base metals have been removed by scrubbing. This
will greatly enhance the efficiency and ease of processing low grade
precious metal-containing chloride solutions.
SUMMARY OF THE INVENTION
The invention relates to the use of a single solvent extraction reagent and
single strip process to produce a concentrated solution of platinum,
palladium and gold from trace levels found in the oxidizing chloride leach
of low grade precious metal containing materials. The recovery of
platinum, palladium and gold from acidic chloride solution is accomplished
by first using an alkylated 8-hydroxyquinoline reagent or any derivative
thereof for extraction wherein a chelate or complex is formed between the
reagent and the precious metals. The chelate or complex is sufficiently
stable to allow extracted base metals to be removed by scrubbing; these
base metals are essentially completely separated from the desired gold,
platinum and palladium. The metal complexes are then separated from the
reagent by acidic thiourea stripping, producing a solution concentrated in
gold, platinum and palladium and essentially free of base metal
contamination
DETAILED DESCRIPTION OF THE INVENTION
As mentioned previously, the present invention relates to a method of
recovering precious metals from aqueous acidic solutions which contain
chloride ions by employing a single solvent extraction reagent and a
single stripping process. The extracting agents employed by the present
invention are able to form a substantially stronger complex with the
precious metals than with base metals. Extracted base metals can be
removed by scrub steps before stripping with acidified thiourea solution.
The acidic solution containing chloride ion can be obtained by leaching a
material containing the precious metals with an acid containing an
oxidizing agent. The chloride feed liquors can result from treatment of
precious metal slimes resulting from the electrolytic refining of copper;
treatment of scrap such as electronic circuit boards; plating effluents;
or refractory gold ore. For example, the precious metal solutions from the
leaching of spent automobile catalytic converters are well suited for this
process.
There are few limitations on the characteristics of the feed liquor for
this process, provided that it contains sufficient amounts of halide ion
to maintain the precious metals as metal complexes in solution. However,
excess amounts of nitrating agents are not recommended since they destroy
the ability of the resins to perform normally.
A preferred embodiment of the invention relates to the use of HCl as the
leaching solution and H.sub.2 O.sub.2 as the oxidizing agent. Other
oxidizing agents may be used in this process including, for example,
chlorine, perchlorate, permanganate, and chlorate. Another preferred
embodiment of the invention is that the platinum should be maintained in a
+4 valence state whereas gold is normally at +3 valence state.
The precious metals treated in the present invention are preferably one or
more of gold, palladium, and platinum, or any mixtures thereof. In another
preferred embodiment of the present invention the leached acidic feed
solution contains platinum and/or palladium. The said process described
herein is substantially effective in the recovery of low concentrations of
precious metals such as those associated with catalytic converters. The
said acid chloride solution can contain from at least 10 to about 1000 ppm
platinum, preferably from about 100 to about 500 ppm platinum, from about
10 to about 5000 ppm palladium and preferably at least 100 to about 1000
ppm palladium, and from about 10 to about 5000 ppm gold, preferably from
about 100 to about 1000 ppm gold.
The acidic feed solution containing any of the precious metals mentioned
above may also contain contaminants such as iron, copper, nickel, cobalt,
cadmium and tin. One important aspect of the current invention is that the
extracting agent is chosen such that it will effectively form a complex or
chelate with a precious metal and allow the less strongly held base metals
to be scrubbed off. Scrubbing is carried out preferably with aqueous HCl
at a pH value of 0-1.5. Thus, this invention will essentially remove
nearly all of the contaminants in the scrubbing process; therefore, less
of these contaminants will interfere in the stripping process.
The precious metals are extracted from these acidic feed liquors by using a
single solvent extraction reagent instead of different reagents required
in prior art studies. Preferably, a phase modifier is also added to
increase the solubility of the metal-loaded extracting agent in the
organic phase. Preferred phase modifiers include long-chain alcohols (e.g.
20 to 40 carbon atoms/ such as tridecyl alcohol. The extracting agent
employed in this invention is an 7-substituted-8-hydroxyquinoline or any
derivative thereof which is of substantially high purity having the
following formula:
##STR1##
wherein R is an alkyl, alkenyl, vinyl, aryl, or cycloalkyl group. The R
group may consist of linear, branched, and cyclic group mentioned herein
containing from about 6 to about 24 carbon atoms. Preferably, the R group
contains from 8 to about 16 carbon atoms. By varying the substituents at
the 7-position of the 8-hydroxyquinoline ring, one can effectively alter
the extraction properties of this reagent. Thus, the modified extracting
agent will more effectively chelate with the precious metals. More
importantly, these extracting agents described herein are able to form
very stable chelates with the precious metals which allow the removal of
base metal contaminants by scrubbing steps prior to stripping with a
single stripping solution.
Once the chelate between the metal ions and extracting agents has been
formed and subsequent base metal scrubbing has removed contaminants, the
precious metals are recovered using an acidified thiourea solution.
The acidified thiourea solution used in this process can have a pH value of
from about -1 to about 4, more preferably from about 0 to about 2. The
thiourea solution can be acidified by using hydrochloric acid up to about
6M in concentration and preferably up to about 3M; or sulfuric acid up to
about 2M. In a most preferred aspect of the current invention, the
thiourea solution is acidified by using 2M HCl. Additionally, the
acidified thiourea solution may contain from about 0.01 to about 3M
thiourea, especially from about 0.1 to about 2M thiourea. In another
preferred embodiment of the invention, the stripping solution contains 1M
thiourea in 2M HCl.
The use of thiourea stripping of precious metals from the
7-alkylated-8-hydroxyquinoline complex is less destructive to the organic
phase than when employing other stripping techniques known in the art such
as hydrolytic or direct hydrogen reduction. The use of the single solvent
extracting process as described herein and combined with the single
stripping step will reduce the overall cost of precious metal recovery.
Additionally, the strip solutions obtained by this process can be treated
chemically to recover metal salts or reduced with hydrogen to produce
metal powders. If the latter is used, the strip solution can be recycled
to the circuit thus making a more economical and efficient means of
extracting and separating precious metals from acid chloride solutions.
The following examples are given to illustrate the invention.
EXAMPLE 1
An organic solution of 10% "Kelex 100" (a commerically available
7-(C.sub.11 -alkylated)-8-hydroxyquinoline), 20% tridecyl alcohol (TDA)
and 70% by volume kerosine was contacted with an equal volume of acidic
leach solution derived from the HCl/H.sub.2 SO.sub.4 leaching of platinum
rich iron getter material from the smelting of industrial catalysts. After
a contact time of two minutes the phases were allowed to separate. The
organic phase was centrifuged to remove entrained aqueous phase and
analyzed for metal content. The organic phase was then contacted with an
equal volume of tap water for two minutes and the phases allowed to
separate. The organic phase was centrifuged and analyzed for metal
content. These steps were then repeated, contacting the organic next with
200 gpl sulfuric acid and then with 4M NaOH as the scrub solutions. The
metal content of the organic after each step is given below ("x"
indicating that metal was present):
______________________________________
Fe Ni Zn Ga Ge Pb Mo Pt
______________________________________
Loaded Org
x x x x x x x x
Water Scrub
x x x x x
Acid Scrub x x x
Caustic Scrub x
______________________________________
Thus, the loaded Kelex solution containing base and rare metals can be
scrubbed to yield an organic solution containing only platinum. This
organic could be stripped by acidic thiourea to produce an enriched
platinum solution free of contamination.
EXAMPLE 2
An organic phase consisting of 15 vol % Kelex 100 and 25 vol % TDA in
kerosine was contacted with an equal volume of 3M HCl containing 10 gpl
ferric ion, 1 gpl cupric ion, and 100 ppm gold, 100 ppm platinum, and 100
ppm palladium. After a two minute contact the phases were separated. The
organic phase was contacted with an equal volume of 200 gpl sulfuric acid.
The raffinate from the extraction step and the organic phase after acid
scrubbing were analyzed. The results are shown in Table 1. The loaded
organic figures are computed as the difference of the raffinate values
from the known feed values.
TABLE 1
______________________________________
Fe (gpl) Cu (gpl) Au (ppm) Pt (ppm)
Pd (ppm)
______________________________________
Feed 10 1 100 100 100
Raffinate
7.3 1 5 N.D.* 3
Loaded 2.7 0 95 100 97
Org
Acid .11 N.D.* 92 94 95
Scrub
Org
______________________________________
*None detected
The data in Table 1 show a hundred-fold decrease in the iron to precious
metal ratio between the feed and the acid scrubbed organic. The organic
extracted essentially all of the precious metals. Little loss in precious
metals content occurred during the acid scrub stage. In this case copper
is not loaded on the organic at 3M HCl acid level.
EXAMPLE 3
An organic solution (5% Kelex 100, 5% TDA, and 90% kerosine) was contacted
with a 1 gpl gold chloride solution. The gold chloride solution was
reagent grade gold chloride made up in 3M HCl. The organic to aqueous
volume ratio was one and contact time was two minutes. Analysis of the
aqueous phase showed complete gold recovery by the organic solution. The
loaded organic was contacted with a 1M solution of thiourea containing 20
gpl sulfuric acid. Equal volume solutions were contacted for two minutes
at room temperature. Organic analysis showed complete stripping of gold to
the thiourea solution. The stripped organic showed no decrease in loading
capacity when contacted with another aliquot of the gold chloride solution
mentioned above. The organic was stripped of gold using the same aliquot
of thiourea solution to build up the gold content. Again, complete
stripping of the organic phase occurred. The acidic thiourea solution was
then reduced by hydrogen at 95.degree. C. and 250 psi for 30 min. A coarse
gold product was filtered off and analysis of the thiourea solution showed
very little gold remaining. The hydrogen reduced thiourea solution proved
effective thereafter in stripping gold from the loaded organic described
above.
EXAMPLE 4
A solution of various platinum group metals and gold was made from standard
solutions to contain 100 ppm for each metal and 2M HCl in acid. This
solution was treated with hydrogen peroxide to ensure that the oxidation
states of the metals would be consistent with oxidized chloride leaching.
An organic solution containing 10% Kelex, 20% TDA, and 70% kerosine was
contacted with the above solution for two minutes. The organic to aqueous
phase volume ratio was 2. The organic was analyzed qualitatively for the
platinum group metals and gold. The organic was then contacted with a pH
1.2 buffer solution for two minutes at a volume ratio of organic to
aqueous of 2. The organic was again analyzed for precious metals. The
organic was then stripped with a 2M HCl solution containing 0.1M thiourea
at an organic-to-aqueous volume ratio of 2. The results are given in Table
2.
TABLE 2
______________________________________
Au Pt Pd Rh Ru Ir Os
______________________________________
Loaded org
++ ++ ++ - + ++ ++
Washed org
++ ++ ++ - - - ++
Stripped org
- + - - - - +
______________________________________
++ Organic fully loaded
+ Organic partially loaded
- Not present in organic
Table 2 shows that all the platinum group metals except rhodium can be
extracted. The ruthenium and iridium can be washed from the organic
leaving only osmium as a potential contaminant for the gold, platinum, and
palladium.
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